I've got a '99 Chevy 3500 that has a water leak on the passenger side. It is coming from the far right side under the dash, but I can't peg it. After pouring water around the area, it seems to be coming in when the water goes between the front right fender and the door jam. From the inside it is coming in from high up on the upper right side of the floor (behind what I would guess is the heater blower). It is coming from really high up, but I don't know where to look.
I really don't want to have to take the dash apart to trace this. But I've been under the truck, down under the hood, under the dash and I'm stumped.

Any suggestions?

Thanks in advance

 

Check the area where the heater core goes through the firewall. There should be some insulation around the pipes to keep the water out.

 

Did you fix your leak? I have a 1998 GMC Z71 and you described my leak exactly. What was your fix? Thanks, Chet

 

Were you able to figure out this problem? I have the same exact issue and cannot figure it out. Please advise. Thank you.

 

It sounds like you might have a leak coming from the cowl area. That’s the space just below the windshield where water drains off. If the drain holes there are clogged, water can build up and leak into the cab.

Here are a few things you can check:

Cowl Drain – Look under the windshield wipers near the bottom of the windshield. There may be leaves or dirt blocking the drain holes. Clean them out if needed.

Seal Around the Blower Motor – The blower motor is on the passenger side, behind the dash. Sometimes the seal around it goes bad, and water leaks through. You can check from under the hood by looking behind the engine on the passenger side.

Door Seal or Fender Seal – Since you said water comes in when you pour it near the fender and door jam, the rubber seals there may be worn or damaged. Check for any gaps or cracks.

Windshield Seal – On older trucks, the seal around the windshield can leak. Check for cracks or loose spots around the glass.

You probably don’t need to take the whole dash apart yet. Try pouring water slowly in each area and watch where it starts to drip inside. You can also use a flashlight and a mirror to look behind things without pulling them out.

Let us know what you find